The "sensor" is simply two metal prongs that touch the coolant.  Current
will flow, but a rather small amount, depending on the type of liquid it
makes contact with.  For any type of likely solution based on water, this
current is enough to tell the circuitry in the dash what's going on.
   If you have a decent ohmmeter, you may be able to measure a resistance
value when you put the  probe in coolant, tho the reading won't actually be
accurate because of chemical reactions that happen when you use DC.  The
Vanagon circuitry uses a type of AC.
   BTW the idea that you must have a 50-50 mixture of water and coolant for
the sensor to work properly is a vanagon list version of an urban myth.
Most any mixture, other than distilled water in a clean container, will be
fine.
   You can learn more than you want to know about this if you go to the
archives and look for:
"coolant resistance thru coolant level probe"  my post from 27 July 2001.

Larry A.

On 9/19/07, Gilles Turmel <gilles.turmel@sympatico.ca> wrote:
>
> Hi,
> I just bought a new sensor. I put it in water and test the continuity
> between the two probes.  Current should flow between the two probes. Yes
> or no?  I don't have any current flowing.  Is the sensor good?
> Best regards.
> Gilles Turmel
>